A technique for fixing a plurality of stacked battery cells by tie bars or bands is known (see, for example, Japanese Patent Application Publication No. 2012-18915 A). In Japanese Patent Application Publication No. 2012-18915 A, although the plurality of battery cells stacked can be effectively suppressed from being deformed by expansion of the battery cells or the like, when external force is applied along the stacking direction of the battery cells, there is a problem that the plurality of battery cells of the battery cell may sometimes be tilted in a chain reaction triggered by the battery cell receiving the external force.